1. Technical Field
The present invention relates to electronic devices and methods for manufacturing the same.
2. Related Art
Electronic devices that include a functional element such as a micro electromechanical system (MEMS) disposed in a cavity portion formed on a substrate are known. A MEMS, such as, for example, a micro resonator, a micro sensor or a micro actuator functions by vibration, deformation and other operations of a micro structure housed in a cavity portion. Therefore, the micro structure is disposed in the cavity portion in a manner that these operations are not disturbed. For example, JP-A-2005-297180 and JP-A-2005-123561 describe methods of forming such a cavity portion.
According to the method described in JP-A-2005-297180, a micro mechanical element is formed on a surface of one substrate, the substrate is then joined in a vacuum chamber with another substrate with an O ring placed between them, and subsequently, a sealant material is filled outside the O ring. According to the method described in JP-A-2005-123561, a MEMS structure is formed on a substrate, a sacrificial layer is then formed on the MES structure, a first sealant member having through holes is further formed on the sacrificial layer, the sacrificial layer is subsequently removed through the through holes of the first sealant member to release a movable part of the MEMS structure, and finally, the through holes of the first sealant member are covered and closed by a second sealant member such as a chemical vapor deposition (CVD) film.
There is a demand for further miniaturization of electronic devices, and the demand consequently requires further reduction of the area occupied by a cavity over a substrate where a functional element is disposed. However, as the device is reduced in size, the cavity and the member with which the cavity is formed are consequently miniaturized, such that the mechanical strength for retaining the cavity may become insufficient. If the strength of the member that forms the cavity is insufficient, for example, the cavity could not be maintained due to mechanical and thermal stress or vibration at the time of mounting, and thus it is feared that the reliability of the electronic device would be lowered.